Conventionally, high cellulose-type gas shielded arc welding electrodes contain a large amount of organic materials such as cellulose, starch, wood flour, etc. as one of the principal components of the coating. Therefore, if a large welding current is applied to the electrode, the electrode is apt to burn. Hence, it has been desired to develop a coated electrode which has sufficient arc strength, sufficient arc spread and deep penetration using relatively low welding current. To this end, it is known that sodium silicate is very effective when used as a binding agent, or as one of the components in the coating material of a coated arc welding electrode. However, sodium silicate is extremely hygroscopic and soluble in water. Thus, if a large amount of sodium silicate is used in the coating material, the coating absorbs much moisture from the atmosphere. When the amount of moisture absorbed exceeds a certain level, the coating itself eventually begins to soften, resulting in deformation of the coating material during the welding operation.
Typical of such conventional compositions are those disclosed in the following patents. U.S. Pat. No. 2,210,777 and 2,209,829, both to General Electric Company, disclose an arc welding electrode of the shielded arc type wherein the moisture resistance of the electrode coating is improved.
U.S. Pat. No. 2,031,494 to Grassell Chemical Co. discloses the use of 30% cellulose (wood flour) and 15% sodium silicate by weight of the total coating material, but said sodium silicate is added as a sodium silicate solution and not as anhydrous sodium silicate.
U.S. Pat. No. 2,052,699 to A. O. Smith discloses the use of 13% cellulose (wood flour) and 42% sodium slicate by weight of the total coating material and the weight ratio of SiO.sub.2 /Na.sub.2 O is 3; however, the sodium silicate is preferably used as water glass according to the disclosure of this patent.
U.S. Pat. No. 2,164,775 to Oxweld Acetylene Co. discloses that its sodium silicate solution contains 56.4% water.
U.S. Pat. No. 2,102,891 to Air Reduction Co. discloses the use of Na.sub.2 O and SiO.sub.2. The weight ratio of SiO.sub.2 /Na.sub.2 O is 3.22. The use of deoxidizing agents in the coating is also disclosed.
U.S. Pat. No. 2,220,954 to Combustion Eng. Co. discloses alpha cellulose as an organic material as well as TiO.sub.2 and iron oxide in a coating composition. U.S. Pat. No. 2,427,966 to Hirschler discloses the use of Fe-Mn, TiO.sub.2 and an organic material containing lignin.
Nevertheless, none of the above-mentioned U.S. Patents specifically discloses the use of anhydrous sodium silicate as one of the ingredients of a coating material for a gas shielded-type coated arc welding electrode. Accordingly, a gas shielded-type arc welding coating electrode having an electrode coating with superior moisture resistance and having superior usability is still desired.